A sensor system includes a femtosecond infrared (fs-IR) laser to generate a laser beam; a reflecting mirror optically receiving the laser beam; a lens optically coupled to the reflecting mirror to focus the laser beam; a phase mask receiving the laser beam from the lens to generate an index modulated pattern; and a few-mode fiber (FMF) receiving the index modulated pattern.

An apparatus for use with a pulsed laser source for forming an optical grating in a target includes an adjustable telescope having an element with a negative optical power, for generation of a diverging optical beam, so that the optical beam has adjustable divergence upon exiting the telescope while focusing of light inside the telescope is avoided. A transmission diffraction grating is disposed in the optical beam exiting the telescope, for forming an optical interference pattern on the target. Optical gratings with different grating periods may be formed by adjusting the divergence of the optical beam exiting the telescope. Lack of tight focal spots inside the telescope enables use of ultrashort pulse duration, high peak intensity laser sources.

Described are optical fibers, e.g., for use in stress-sensing or shape-sensing applications, that use overlapping grating configurations with chirped gratings to facilitate strain delay registration. In accordance with various embodiments, a fiber core may, for instance, have two overlapping sets of chirped gratings that differ in the direction of the chirp between the first and second sets, or a set of chirped gratings overlapping with a single-frequency grating. Also described are strain sensing systems and associated computational methods employing optical fibers with overlapping gratings.

An endoscope can include an elongated endoscope body. An optical fiber can extend along the endoscope body. The optical fiber can direct therapeutic light and illumination light longitudinally along the optical fiber to a distal portion of the endoscope body. The therapeutic light and the illumination light can have different wavelengths. A wavelength-sensitive light separator, disposed at a distal portion of the optical fiber, can direct the illumination light to exit the optical fiber laterally through a lateral side of the optical fiber at the distal portion of the optical fiber and permit the therapeutic light to exit the optical fiber longitudinally through a distal end of the optical fiber. Examples of suitable wavelength-sensitive light separators can include one or more fiber Bragg gratings that can be obliquely angled, or a diffraction grating disposed on a lateral edge of a length of coreless fiber.

Provided are an apparatus for manufacturing a grating and a method for manufacturing a grating with which a grating having a desired attenuate wavelength characteristic can be easily manufactured. The apparatus, which forms a grating in an optical fiber as an optical waveguide, includes a laser source, beam diameter adjusting means, a scanning mirror, mirror position adjusting means, a cylindrical lens, lens position adjusting means, a phase mask, mask position adjusting means, a stage, a fixing jig, and a synchronous controller. The synchronous controller controls an adjustment of a position of the scanning mirror performed by the mirror position adjusting means and an adjustment of a position of the phase mask performed by the mask position adjusting means in a manner in which they are associated with each other.

A method of, and apparatus for, inscribing a grating in an optical waveguide so as to reduce transverse inscription variations, are provided. The waveguide is exposed to multiple beams or interference patterns of actinic radiation from multiple azimuthal directions. The beams of actinic radiation are preferably split into a plurality of beams that have wave vectors with different longitudinal components, e.g., via gratings such as phase masks. The periods and phases of the interference patterns of the beams of actinic radiation are preferably matched. A control beam may be provided that does not hit the waveguide. A control loop optionally controls at least one of the position or orientation of at least one of the beams of actinic radiation. The gratings are, for example, Bragg gratings.

Methods and systems for writing a Bragg grating along a grating region of an optical fiber through a polymer coating of the optical fiber are provided. A light beam of ultrafast optical pulses is impinged on the grating region, the ultrafast optical pulses being characterised by writing wavelength at the grating region to which the polymer coating is substantially transparent The light beam is diffracted through a phase mask so as to form an interference pattern defining the Bragg grating at the grating region of the optical fiber. The light beam is also focussed such that the intensity of the optical pulses is below a damage threshold within the polymer coating, and above an FBG inscription threshold within the grating region of the fiber. Optical fiber having Bragg gratings and improved mechanical are also provided.

The disclosed embodiments provide systems and methods for mitigating lensing and scattering as an optical fiber is being inscribed with a grating. The disclosed systems and methods mitigate the lensing phenomenon by surrounding an optical fiber with an index-matching material that is held in a vessel with a sealed phase mask. The sealed phase mask allows it to be in contact with a liquid index-matching material without having the liquid index-matching material seep into the grooves of the sealed phase mask. Thus, for some embodiments, the sealed phase mask may be immersed in a liquid index-matching material without adversely affecting the function of the phase mask.

In various embodiments, an optical fiber includes a core having a relatively large area selected so as to raise a threshold of stimulated Raman scattering or stimulated Brillouin scattering, or both, the core having a high aspect ratio elongated cross-section and having a first refractive index. The core is narrower in a fast-axis direction and wider in a slow-axis direction, such that the fiber is mechanically flexible in the fast-axis direction and is mechanically rigid in the slow-axis direction.

A method and apparatus for inscribing a high-temperature stable Bragg grating in an optical waveguide, comprising the steps of: providing the optical waveguide; providing electromagnetic radiation from an ultrashort pulse duration laser, wherein the wavelength of the electromagnetic radiation has a characteristic wavelength in the wavelength range from 150 nanometers (nm) to 2.0 micrometers (m); providing cylindrical focusing optics; providing a diffractive optical element that when exposed to the focused ultrashort laser pulse, creates an interference pattern on the optical waveguide, wherein the irradiation step comprises irradiating a surface of the diffractive optical element with the focused electromagnetic radiation, the electromagnetic radiation incident on the optical waveguide, from the diffractive optical element, being sufficiently intensive to cause permanent (Type II) change in the index of refraction within multiple Bragg grating planes in the core of the optical waveguide resulting from at least one micropore.